Manufacturing method of semiconductor device

ABSTRACT

In view of the problem that an organic semiconductor layer of an organic TFT is likely to deteriorate due to water, light, oxygen, or the like, it is an object of the present invention to simplify a manufacturing step and to provide a method for manufacturing a semiconductor device having an organic TFT with high reliability. According to the invention, a semiconductor layer containing an organic material is formed by patterning using a mask, and thus an organic TFT is completed in the state where the mask is not removed but to remain over the semiconductor layer. In addition, a semiconductor layer can be protected from deterioration due to water, light, oxygen, or the like by using the remaining mask.

TECHNICAL FIELD

The present invention relates to a semiconductor device having anorganic thin film transistor and a manufacturing method thereof.

BACKGROUND ART

Nowadays, a technique for making up a thin film transistor (TFT) with asemiconductor thin film (thickness of approximately from severalnanometers to several hundred nanometers) formed over a substrate havingan insulating surface attracts attention. A thin film transistor iswidely applied to an electronic device such as an IC and anelectro-optic device. In particular, a thin film transistor has beenrushed to be developed as a switching element of a display device.

The study of a thin film transistor using an organic semiconductor(hereinafter, referred to as “organic TFT”) among TFTs is proceeding. Anorganic TFT has good flexibility since an organic material is used. Inaddition, an organic TFT can be formed at lower temperature comparedwith a TFT using an inorganic semiconductor; therefore, a resin materialsuch as plastic can be used for a substrate. As a result, a device whichis lightweight and flexible can be obtained. An organic TFT is not onlyable to be expected to simplify a process by using a printing method, anink-jet method, a vapor deposition method, and the like but able tosuppress a manufacturing cost since an inexpensive material for asubstrate can be used; therefore, it can be estimated that there is anadvantage in respect of costs.

An organic TFT has a disadvantage that deterioration of an electriccharacteristic is caused if an organic TFT is left in an atmospheric airsince an organic semiconductor is oxidized or decomposed by beingexposed to water or oxygen. Therefore, as in Patent Document 1 (PatentDocument 1: Patent Laid-Open No. 2003-324202), an insulating film isformed over a semiconductor layer of an organic TFT to protect thesemiconductor layer by the insulating film to reduce the deteriorationdue to water, light, or oxygen.

DISCLOSURE OF INVENTION

However, one manufacturing step is added to manufacturing steps of a TFTwhen an insulating film for covering a semiconductor layer of an organicTFT is formed.

Further, also in the case of forming a plurality of organic TFTs havingdifferent conductivity over the same substrate, a semiconductor filmformed in advance is required to be covered with an insulating film orthe like so that the semiconductor film of an organic TFT having onetype of conductivity formed in advance is not etched along withpatterning of a semiconductor film having the other type of conductivityformed afterward. Therefore, a step of forming an insulating film newlyover the semiconductor film formed in advance is required.

On the other hand, in the case of forming an organic semiconductor layerby patterning, there is a step of removing a mask which is used for thepatterning. In general, a mask is formed of an organic insulating filmsuch as polyvinyl; therefore, the mask is removed by wet etching. Afterremoving the mask, the surface of an organic semiconductor layer iswashed to wash away etchant remaining over the surface of the organicsemiconductor layer. Hence, it is highly likely that water penetratesinto the organic semiconductor layer in this step; therefore, the stepis not favorable for the organic semiconductor layer. The mask materialand the organic semiconductor layer material are organic materials;therefore, it is difficult to obtain large selectivity between theorganic semiconductor material and the mask when the mask is removed. Itis required to select materials for the organic semiconductor and themask in order to obtain large selectivity; therefore, there is alimitation in selecting a material.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is an object of the presentinvention to simplify a manufacturing step. Moreover, it is an object ofthe invention to provide a method for manufacturing a semiconductordevice having an organic TFT with high reliability.

One feature of the invention is that a semiconductor layer containing anorganic material is formed by patterning using a mask to complete a TFTin the state where the mask is not removed to remain over thesemiconductor layer. One feature of the invention is to protect thesemiconductor layer from deterioration due to water, light, oxygen, orthe like using the remaining mask.

One feature of the invention is that a semiconductor layer having onetype of conductivity is formed by patterning using a mask when P typeand N type organic TFTs are formed over the same substrate, then asemiconductor layer having the other type of conductivity is formed bypatterning using a mask with the mask remaining over the semiconductorlayer. That is, one feature of the invention is to complete each organicTFT with a mask remaining over each semiconductor layer.

One feature of the invention is to form a mask which is to be formedover a semiconductor layer by a method which gives the lowersemiconductor layer less physical damage, such as a droplet dischargemethod. One feature of the invention is to provide a barrier layerformed of an inorganic film between a remaining mask and a semiconductorlayer containing an organic material. Note that a droplet dischargemethod in this specification is a method for forming a film using an inkjet device or a dispenser device.

According to the invention, a manufacturing step can be simplified andan organic TFT can be prevented from deterioration due to water, light,or oxygen, and thus an organic TFT with high reliability can beobtained. Further, the problem on selectivity of etchant in a step ofremoving a mask is not required to be considered since the mask is notremoved, and thus the material of an organic semiconductor and a maskcan be freely selected.

Wet etching which is frequently used for removing a mask and washing ofthe surface of an organic semiconductor layer after etching can beomitted since there is no step of removing a mask. Hence, a step inwhich water is likely to penetrate into an organic semiconductor layermost can be omitted, and this is greatly effective for preventing anorganic semiconductor layer from deterioration.

When the invention is applied to the formation of organic TFTs havingdifferent conductivity, a semiconductor film containing an organicmaterial having one type of conductivity can be patterned in the statewhere there is a mask over a semiconductor layer containing an organicmaterial having the other type of conductivity. Therefore, etching ofthe surface of the semiconductor layer having the other type ofconductivity by the patterning can be prevented. In addition,unnecessary reduction of a film in a semiconductor layer and physicaldamage to a semiconductor layer can be prevented.

A semiconductor layer can be protected from water, light, oxygen, or thelike from external environment more certainly by providing a barrierlayer between the semiconductor layer and a mask. Water can be preventedfrom penetrating into the semiconductor layer by a barrier layer even inthe case where the mask retains water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E are explanatory views of a manufacturing step of asemiconductor device according to the present invention;

FIG. 2 is an explanatory view of a semiconductor device according to theinvention;

FIGS. 3A to 3D are explanatory views of a manufacturing step of asemiconductor device according to the invention;

FIGS. 4A to 4E are explanatory views of a manufacturing step of asemiconductor device according to the invention;

FIGS. 5A to 5D are explanatory views of a manufacturing step of asemiconductor device according to the invention;

FIGS. 6A and 6B are explanatory views of a manufacturing step of asemiconductor device according to the invention;

FIGS. 7A and 7B are a top view and a circuit diagram of a display deviceaccording to the invention;

FIGS. 8A and 8B are explanatory views of a manufacturing step of asemiconductor device according to the invention;

FIGS. 9A and 9B are explanatory views of semiconductor devices accordingto the invention;

FIGS. 10A to 10C are explanatory views of a manufacturing step of asemiconductor device according to the invention;

FIGS. 11A and 11B are views of display devices using the invention;

FIGS. 12A and 12B are views of a display device having an electronic inkusing the invention;

FIGS. 13A to 13C are electronic devices each provided with asemiconductor device according to the invention; and

FIGS. 14A to 14C are electronic devices each provided with asemiconductor device according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment modes according to the present invention are described indetail with reference to the drawings. However, it is easily understoodby those skilled in the art that embodiments and details hereindisclosed can be modified in various ways without departing from thepurpose and the scope of the present invention. Therefore, it should benoted that the description of embodiment modes to be given below shouldnot be interpreted as limiting the present invention. In addition, thesame reference numeral is given to a common portion in each drawing, anddetailed description is omitted.

Embodiment Mode 1

In this embodiment mode, a manufacturing method of an organic TFTaccording to the present invention is explained with reference to FIGS.1A to 1E.

A substrate 101 having an insulating surface is prepared as shown inFIG. 1A. A glass substrate, a quartz substrate, or a substrate formedfrom an insulating substance such as alumina can be used as thissubstrate 101. In addition, a substrate having flexibility may be used,and a substrate comprising one selected from polyethylene terephthalate(PET), polyethylenenaphthalate (PEN), polyethersulfone (PES),polycarbonate (PC), polyimide, and the like may be used.

Then, a gate electrode 102 of a TFT is formed over the substrate 101using a material having conductivity by a droplet discharge method, aprinting method, an electric field plating method, a PVD (Physical VaporDeposition) method, a CVD (Chemical Vapor Deposition) method, a vapordeposition method, or the like. The film thickness of the gate electrode102 is preferably from 100 nm to 500 nm. In the case of using a PVDmethod, a CVD method, a vapor deposition method, or the like, the gateelectrode 102 is formed to be etched in a desired shape afterdeposition.

As a material having conductivity, metal such as Ag, Au, Cu, Ni, Pt, Pd,Ir, Rh, W, Al, Ta, Mo, Cd, Zn, Fe, Ti, Si, Ge, Zr, or Ba; indium tinoxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), zinc oxide (GZO)added with gallium, or indium tin oxide containing silicon oxide, eachof which is used as a transparent conductive film; organic indium;organic tin; titanium nitride (TiN); or the like is appropriately used.In addition, a conductive layer formed from any of these materials maybe stacked.

In the case of forming a gate electrode by a droplet discharge method, acomposition in which a conductor is dissolved or dispersed in a solventis used for a composition which is to be discharged from a dischargeopening. Metal of the material having conductivity, a fine particle ofsilver halide, or a dispersant nanoparticle can be used as theconductor.

As for the composition to be discharged from a discharge opening, it ispreferable to use any material of gold, silver, and copper dissolved ordispersed in a solvent in consideration of a specific resistance value.It is more preferable to use silver or copper which has low resistanceand is inexpensive. As for the solvent, esters such as butyl acetate orethyl acetate; alcohols such as isopropyl alcohol or ethyl alcohol;methyl ethyl ketone; an organic solvent such as acetone; or the like maybe used.

The viscosity of the composition used for a droplet discharge method ispreferably in the range of 5 mPa·s to 20 mPa·s to prevent thecomposition from drying and to discharge the composition smoothly from adischarge opening. The surface tension is preferably 40 m/N or less.Note that the viscosity of the composition and the like may beappropriately adjusted in accordance with a solvent to be used and anintended use. For example, the viscosity of a composition in which ITO,ZnO, IZO, GZO, indium tin oxide containing silicon oxide, organicindium, organic tin, or the like is dissolved or dispersed in a solventis 5 mPa·s to 20 mPa·s, the viscosity of a composition in which silveris dissolved or dispersed in a solvent is 5 mPa·s to 20 mPa·s, and theviscosity of a composition in which gold is dissolved or dispersed in asolvent is 10 mPa·s to 20 mPa·s.

The diameter of a particle of the conductor is preferably made as smallas possible for the purpose of preventing a clogged nozzle and formanufacturing a high-definition pattern, although the diameter of eachnozzle depends on a desired shape of a pattern and the like. Preferably,the diameter of the particle of the conductor is 0.1 μm or less. Thecomposition is formed by a known method such as an electrolytic method,an atomization method, a wet reduction method, or the like, and ingeneral, the particle size thereof is approximately 0.5 μm to 10 μm.However, when a gas evaporation method is employed, a nanoparticleprotected by a dispersant is minute, approximately 7 nm. When eachsurface of nanoparticles is covered with a coating, the nanoparticles donot cohere in the solvent and are stably dispersed in the solvent atroom temperature, and show a property similar to that of liquid.Accordingly, it is preferable to use a coating.

The step of discharging the composition may be performed under reducedpressure. This is because the solvent of the composition is vaporizedduring a period from the point of discharging to the point of landing onan object to be treated, and thus, later steps of drying and baking canbe omitted or shortened. After discharging the solution, either or bothsteps of drying and baking is/are performed under atmospheric pressureor reduced pressure according to the solution by laser lightirradiation, rapid thermal annealing, a heating furnace, or the like.Each step of drying and baking is a step of heat treatment. For example,drying is performed for three minutes at 100° C. and baking is performedfor 15 minutes to 120 minutes at temperatures of from 200° C. to 350°C., each of which has a different purpose, temperature, and period. Thesubstrate may be heated to favorably perform the steps of drying andbaking. The temperature of heating the substrate at the time depends ona material of the substrate or the like, but it is set at 100° C. to800° C. (preferably, 200° C. to 350° C.). According to the steps, fusionand welding among conductive particles are accelerated by vaporizing thesolvent in the solution or chemically removing a dispersant and curingand shrinking a resin around the conductive particle. The steps ofdrying or baking are performed in an oxygen atmosphere, a nitrogenatmosphere, or an atmospheric air. The steps are preferably performed inan oxygen atmosphere where the solvent in the solution is likely tovaporize. However, a binder formed from an organic substance remains inthe conductive layer according to the heating temperature, atmosphere,or period.

In this embodiment mode, a conductive layer containing silver as itsmain component is formed as the gate electrode by selectivelydischarging a solution dispersed with silver particles of severalnanometers (hereinafter referred to as “Ag paste”) and drying and bakingthe same.

Subsequently, a gate insulating film 103 having a film thickness of from100 nm to 400 nm is formed over the gate electrode 102. The gateinsulating film 103 can be formed to have a single layer structure or astacked layer structure of an insulating film containing siliconnitride, silicon oxide, or an other insulating film containing siliconby a thin film formation method such as a plasma CVD method or asputtering method. The gate insulating film 103 preferably has a stackedlayer structure of a silicon nitride film (silicon nitride oxide film),a silicon oxide film, and a silicon nitride film (silicon nitride oxidefilm) from the side being in contact with the gate electrode. Since thegate electrode is in contact with a silicon nitride film or a siliconnitride oxide film in this structure, deterioration of the gateelectrode due to oxidation can be prevented.

Alternatively, the gate insulating film 103 can be formed using aninsulating solution by a droplet discharge method, a coating method, asol-gel method, or the like. As a typical example of the insulatingsolution, a solution dispersed with inorganic oxide particles,polyimide, polyamide, polyester, acrylic, PSG (phosphorous glass), BPSG(phosphorous boron glass), silicate-based SOG (Spin on Glass), alkoxysilicate-based SOG, polysilazane-based SOG, and SiO₂ including a Si—CH₃bond typified by polymethyl siloxane can be appropriately used.

Next, as shown in FIG. 1B, source and drain electrodes 104 and 104′ areformed over the gate insulating film 103 using a conductive material.The source and drain electrodes can be formed by the similar materialand method as those of the gate electrode 102, and the film thicknessesthereof are preferably 300 nm to 800 nm. Here, the source and drainelectrodes 104 and 104′ are formed by selectively discharging solutionof Ag paste dispersed with silver particles of several nanometers and bydrying.

Then, as shown in FIG. 1C, a semiconductor film 105 is formed from anorganic semiconductor material over the source and drain electrodes 104and 104′ by a printing method, a spray method, a spin-coating method, adroplet discharge method, a vapor deposition method, a CVD method, orthe like. Since the semiconductor film 105 may be a size larger than adesired semiconductor layer, the semiconductor layer 105 may be formedover the whole surface as shown in FIG. 1C or may be formed not over thewhole surface but a part of a region as shown in FIG. 1D.

When a high molecular weight based material is used among organicsemiconductor materials, a dipping method, a casting method, a barcoating method, a spin coating method, a spray method, an ink-jetmethod, or a printing method may be appropriately used. An organicmolecular crystal or an organic high molecular weight compound materialmay be used as an organic semiconductor material. As a specific organicmolecular crystal, a polycyclic aromatic compound, conjugated doublebond-based compound, carotene, a macrocycle compound or a complexthereof, phthalocyanine, a charge transfer complex (CT complex), a TTF(tetrathiofulvalene):TCNQ (tetracyanoquinodimethane) complex, a freeradical, diphenylpicrylhydrazyl, pigment, and protein can be given. Onthe other hand, as a specific organic high molecular weight compoundmaterial, a high molecular weight material such as a π-conjugatedpolymer (high molecular weight), polyvinilpyridine, an iodide complex, aphthalocyanine metal complex, or the like can be given. Especially, itis preferable to use a π-conjugated polymer (high molecular weight)having a skeleton including a conjugated double bond such aspolyacetyrene, polyaniline, polypyrrole, polythienylene, polythiophenederivatives, poly(3-hexylthiophene) [P3HT, that is, a high molecularweight material that alkyl group of polythiophene derivatives in whichflexible alkyl group is introduced to three positions of polythiopheneis hexyl group], poly(3-alkylthiophene), poly(3-docosylthiophene),polyparaphenylene derivatives, or polyparaphenylene vinylenederivatives.

An organic semiconductor film formed from a low molecular weight basedmaterial may be formed by a vapor deposition method. For example, athiophene oligomer film (degree of polymerization is 6) or a pentacenefilm may be formed by a vapor deposition method.

In particular, in the case where the substrate 101 is a large substrate,full of flexibility, or the like, the organic semiconductor film ispreferably formed by the method of dropping a solution. Then, a solventis made to vaporize by leaving naturally or baking to form thesemiconductor film 105. The semiconductor film 105 preferably has a filmthickness of from 20 nm to 100 nm, and the film thickness thereof is setto be 50 nm here.

Then, a mask 106 is formed from an insulating material to have a filmthickness of from 400 nm to 2 μm so as to be in contact with thesemiconductor film 105. One feature of the invention is to form a maskby a method without physical damage to the semiconductor film 105, thatis, by a method or the like for exposing light using a photomask afterbeing formed by a droplet discharge method, a printing method, and adroplet discharge method. These methods for forming a mask are extremelyfavorable since physical damage to the semiconductor film 105 is lessthan that of a plasma method or a sputtering method.

A heat-resistant high molecular weight material is preferably used as aninsulating material, and a high molecular weight material which has anaromatic ring or a heterocyclic ring as a main chain and includes atleast a highly polar heteroatom group in an aliphatic portion can beused. As typical examples of such high molecular weight substances,polyvinyl alcohol (PVA), acrylic, siloxane, polyimide, and the like canbe given. When a photo mask is used as the mask 106, a photosensitiveresin material such as an epoxy resin, a phenol resin, a novolac resin,an acrylic resin, a melamine resin, a urethane resin, or the like isused as an insulating film of a photosensitive resin. In addition,photosensitive organic materials such as benzocyclobutene, parylene,flare, and polyimide can also be used. As typical positivephotosensitive resins, a photosensitive resin having a novolac resin anda naphthoquinonediazide compound as a photosensitive agent can be given,while as typical negative photosensitive resins, a photosensitive resinhaving a base resin, diphenylsilanediol, an acid generating agent, andthe like can be given. When an organic material is used for a mask, theunevenness of a semiconductor film in a lower layer is hardly reflecteddue to its superior planarity; therefore, the film thickness of a filmformed over the mask can be uniform and disconnection can be alsoprevented.

When the mask is formed by a droplet discharge method, an object inwhich the above insulating material is dissolved or dispersed into asolvent is used as a compound which is to be discharged from a dischargeopening.

Then, the semiconductor film 105 is patterned using the mask 106 to forma semiconductor layer 107 as shown in FIG. 1E. As a patterning method,there are O₂ ashing, O₃ ashing, and the like. In the case where the maskis formed from an organic material, the mask is etched in some degree aswell as the semiconductor layer when the patterning is performed.However, the film thickness of the mask is extremely thick compared withthat of the semiconductor layer and etching of the mask is not aproblem; therefore, etching selectivity between the mask and the organicsemiconductor layer is not required to consider so much. The mask 106 isnot removed to remain over the semiconductor layer 107, and thus anorganic TFT is completed. After completing the organic TFT, aninsulating film, a passivation film, and the like are formed above theTFT to form a semiconductor device.

Thus, one step of removing a mask can be eliminated, and the penetrationof moisture into the semiconductor layer associated with the removal ofa mask can be prevented by completing an organic TFT without removing amask used for the patterning of a semiconductor layer. Physicalinfluence such as deterioration caused by light, oxygen, moisture, orthe like and etching can be prevented by making a mask remain over thesemiconductor layer, and the remaining mask can be made to serve as aprotective film of the organic semiconductor layer.

In the above step, the semiconductor layer is formed after forming thesource and drain electrodes to complete the organic TFT. Alternatively,the semiconductor layer 107 formed using an organic semiconductormaterial may be formed after forming the gate insulating film 103, andthe source and drain electrodes 104 and 104′ may be formed thereafter.FIG. 2 shows a cross-sectional view of an organic TFT according to theinvention formed by this step.

In the case of FIG. 2, a contact region of the semiconductor layer 107and the source and drain electrodes 104 and 104′ becomes reduced sincethe mask 106 remains. Therefore, the semiconductor film may be patternedin a reverse tapered shape when the semiconductor film is patterned.According to this, the contact region of the semiconductor layer and thesource and drain electrodes become larger, and also, disconnection ofthe source and drain electrodes can be prevented.

In the case where the source and drain electrodes are formed afterforming the semiconductor layer, the semiconductor layer may beinfluenced by plasma, vapor deposition, sputtering, or the like when thesource and drain electrodes are formed. However, by applying theinvention, the semiconductor layer is protected from the influence ofplasma, vapor deposition, sputtering, or the like by a mask; therefore,the semiconductor layer can be prevented from being physically damaged.

Embodiment Mode 2

In this embodiment mode, a method for forming a top gate organic TFT isexplained with reference to FIGS. 3A to 3D. In FIGS. 3A to 3D, as forthe same reference numerals as in Embodiment Mode 1, the material, theforming method, and the like are referred to the description inEmbodiment Mode 1.

Source and drain electrodes 104 and 104′ are formed over a substrate101. Then, a semiconductor film 105 containing an organic material isformed over the substrate 101 and the source and drain electrodes, andthen, a mask 106 is formed so as to be in contact with the semiconductorfilm 105 (FIGS. 3A and 3B).

Next, as shown in FIG. 3C, the semiconductor film 105 is patterned usingthe mask 106 to form a semiconductor layer 107. Subsequently, a gateelectrode 102 is formed over the mask 106 in the state where the mask106 is not removed to remain (FIG. 3D). In this embodiment mode, themask 106 serves as both a protective film of the semiconductor layer 107and a gate insulating film.

A top gate organic TFT is completed with the mask 106 remaining over thesemiconductor layer 107 as in this embodiment mode, and thus a step offorming a gate insulating film is eliminated, and physical influencesuch as plasma or sputtering on the semiconductor layer 107 when a gateinsulating film is formed can be eliminated. In addition, deteriorationof the semiconductor layer 107 caused by water, light, oxygen, or thelike from outside can be prevented.

Embodiment Mode 3

In this embodiment mode, a method for forming a first element which isan N type organic TFT and a second element which is a P type organic TFTsimultaneously is explained with reference to FIGS. 4A to 4E. In FIGS.4A to 4E, as for a substrate, a gate electrode, a gate insulating film,source and drain electrodes, a mask, a semiconductor film, asemiconductor layer, and the like having the same reference numerals asin Embodiment Mode 1, the material, the forming method, and the likethereof are referred to the description in Embodiment Mode 1.

A gate electrode 102 a of a first element and a gate electrode 102 b ofa second element are formed over a substrate 101 in FIG. 4A. Then, agate insulating film 103 is formed over the gate electrode 102 a of thefirst element and the gate electrode 102 b of the second element.Further, source and drain electrodes 104 and 104 a′ of the firstelement, and source and drain electrodes 104 b and 104 b′ of the secondelement are formed over the gate insulating film 103.

Subsequently, as shown in FIG. 4B, a first semiconductor film 105 a isformed over the source and drain electrodes of the first and secondelements. As for the first semiconductor film 105 a, any of an N typeorganic semiconductor material and a P type organic semiconductormaterial may be used, and an N type organic semiconductor material isused here. As for the specific N type organic semiconductor material,any of materials can be used within the operating range of an N typeorganic TFT which is to be completed. The first semiconductor film 105 amay be formed over the whole surface as shown in FIG. 4B or may bepartially formed in a region to which an N type semiconductor layer isformed as shown in FIG. 1D.

Next, a first mask 106 a is formed over the first semiconductor film 105a and the first semiconductor film 105 a is patterned using the firstmask to form a semiconductor layer 107 a of the first element (FIG. 4C).

Then, as shown in FIG. 4D, a second semiconductor film 105 b formed froma P type organic semiconductor material is formed with the first maskremaining over the semiconductor layer 107 a. As for the P type organicsemiconductor material, any of materials can be used within theoperating range of a P type organic TFT which is to be completed, andpentacene is used here. A second mask 106 b is formed over the secondsemiconductor film 105 b, and the second semiconductor film is patternedusing the second mask. At this time, the first mask 106 a remains overthe semiconductor layer 107 a; therefore, the semiconductor layer 107 acan be prevented from being physically damaged when the secondsemiconductor film is patterned.

According to the above, the first element and the second element arecompleted by forming a semiconductor layer 107 b of the P type organicTFT which is the second element, and the N type organic TFT and the Ptype organic TFT can be formed over the same substrate (FIG. 4E). Inaddition, a complementary TFT may include the N type organic TFT and theP type organic TFT formed according to this embodiment mode.

In the case of forming the N type and P type organic TFTs over onesubstrate, a step of forming the N type organic semiconductor layer anda step of forming the P type organic semiconductor layer are required tobe separately provided. Therefore, an organic semiconductor layer havingone type of conductivity formed in advance is physically damaged in somecases. In addition, there is not so much difference in etching ratesince both of the organic semiconductor layers contain organicmaterials; therefore, an organic semiconductor layer having one type ofconductivity formed in advance is drastically etched in some cases whilethe patterning of the other organic semiconductor layer is performed.

However, according to the invention, physical influence on an organicsemiconductor layer formed in advance caused by patterning an organicsemiconductor layer formed afterward can be reduced since the organicsemiconductor layer formed in advance is protected by a mask remainingthereover. Furthermore, a mask used for the patterning can be utilizedas a protective film; therefore, the number of steps is not required toincrease newly, and conversely, a step of removing a mask can beomitted, and thus a manufacturing step can be substantially reduced.Moreover, the penetration of light, heat, oxygen, or the like into anorganic semiconductor layer can be prevented by a mask which serves as aprotective film, and thus an organic TFT with high reliability can beprovided.

This embodiment mode explains a step of forming an organic semiconductorlayer after forming source and drain electrodes as shown in FIGS. 1A to1E in Embodiment Mode 1. However, it is obvious that, as shown in FIG.2, source and drain electrodes may be formed after forming asemiconductor layer or N type and P type organic TFTs may be formed soas to have a top gate structure in Embodiment Mode 2.

Embodiment Mode 4

In this embodiment mode, an N type organic TFT and a P type organic TFTincluded in one pixel of an electroluminescence (EL) display device areexplained with reference to FIGS. 5A to 7B. In FIGS. 5A to 7B, as forthe same reference numerals as in Embodiment Modes 1 to 3, the material,the forming method, and the like thereof are referred to the descriptionin Embodiment Modes 1 to 3.

First, a gate electrode 102 a of a first element is formed over asubstrate 101. As for the first element, any of an N type organic TFTand a P type organic TFT may be used, and an N type organic TFT is usedhere. A gate insulating film 103 a, source and drain electrodes 104 aand 104 a′ are formed over the gate electrode 102 a of the first element(FIG. 5A). Then, a first semiconductor film 105 a containing an N typeorganic semiconductor material and a first mask 106 a are formed (FIG.5B). Here, the first semiconductor film 105 a is partially formed;however, the first semiconductor film 105 a may be formed over the wholesurface.

The first semiconductor film is etched using the first mask to form asemiconductor layer 107 a containing an N type organic material of thefirst element. At this stage, the first element having the gateelectrode 102 a, the gate insulating film 103 a, the source and drainelectrodes 104 a and 104 a′, and the semiconductor layer 107 acontaining an organic material is formed (FIG. 5C).

Then, as shown in FIG. 5D, a second element which is a P type organicTFT is formed. A gate insulating film 103 b, source and drain electrodes104 b and 104 b′, a second semiconductor film 105 b containing a P typeorganic semiconductor material, and a second mask 106 b of the secondelement are sequentially formed. Here, the second semiconductor film 105b is partially formed: however, the second semiconductor film 105 b maybe formed over the whole surface. The second semiconductor film isetched using the second mask to form a semiconductor layer 107 bcontaining a P type organic material of the second element. According tothe above steps, an N type organic TFT 601 and a P type organic TFT 602are formed (FIG. 6A).

And then, as shown in FIG. 6B, an insulating film 603 is formed. Any ofan inorganic film and an organic film may be used as the insulatingfilm. Continuously, a wiring 604 which is connected to the drainelectrode 104 b′ of the P type organic TFT 602 is formed, and aconductive layer 605 is formed so as to be connected to the wiring.Then, an insulating layer 606 which is to be an embankment is formed,and an electroluminescent layer 607 and a conductive layer 608 arestacked so as to be in contact with the conductive layer 605. In theabove structure, the conductive layer 605 corresponds to an anode andthe conductive layer 608 corresponds to a cathode since a TFT whichdrives a light emitting element is the P type organic TFT. In addition,light from a light emitting element is emitted toward the substrate 101side, that is, a bottom emission structure. However, the structure of anEL element in this embodiment mode, any structure may be used if lightis emitted using the N type organic TFT 601 and the P type organic TFT602, and the structure is not limited to the structure of the EL elementillustrated in this embodiment mode.

According to the above steps, a display device which drives an ELelement by the P type and N type organic TFTs is completed. The drainelectrode 104 a′ of the first element can also serves as a gateelectrode of the second element by manufacturing a display deviceaccording to the method in this embodiment mode. Therefore, a step ofelectrically connecting the drain electrode of the first element an thegate electrode of the second element can be omitted and a manufacturingprocess can be shortened.

In this embodiment mode, a bottom gate structure is employed for thefirst element and the second element; however, the structure is notlimited thereto, and the first element may be a top gate structure andthe second element may be a bottom gate structure. Also in this case,one of the source and drain electrodes of the first element can alsoserves as the gate electrode of the second element.

FIG. 7A shows a top view of a pixel portion of the display devicemanufactured according to this embodiment mode and FIG. 7B shows acircuit diagram thereof. FIG. 6B is a cross-sectional view taken alongline A-A′ of a pixel portion of the display device of FIG. 7A. Referencenumeral 701 shown in FIG. 7B denotes an EL element, which includes theconductive layers 605 and 608 and the electroluminescent layer 607 inFIG. 6B.

The present invention can be freely combined with Embodiment Mode 1 to 3within the range of enablement.

Embodiment Mode 5

In this embodiment mode, a structure provided with a barrier layerbetween an organic semiconductor layer and a mask which is to be aprotective film thereof in Embodiment Modes 1 to 4 is explained withreference to FIGS. 8A and 8B.

As shown in FIG. 8A, steps up to the formation of source and drainelectrodes of a bottom gate TFT over a substrate are similar to thoseshown in FIGS. 1A and 1B in Embodiment Mode 1. Then, after forming asemiconductor film 105 containing an organic material, an inorganic film801 is formed so as to be in contact with the semiconductor film 105.The inorganic film is formed of a silicon oxide film, a silicon nitridefilm, or a silicon oxynitride film, or a stacked film including at leasttwo layers thereof. A CVD method, a sputtering method, a vapordeposition method, a droplet discharge method, printing method, or thelike can be used as a method for forming the inorganic film. Consideringphysical damage to the semiconductor film, a droplet discharge method, aprinting method, or the like is preferably used as a method for formingthe inorganic film 801.

Next, a mask 106 is formed so as to be in contact with the inorganicfilm 801 to etch the inorganic film 801 and the semiconductor film 105using the mask 106 as shown in FIG. 8B. The inorganic film 801 isfirstly etched using the mask 106, then the semiconductor film 105 isetched using the mask 106. An organic TFT having a barrier layer 802between a semiconductor layer 107 and the mask 106 is completed by theetching. The barrier layer also serves as a protective film of thesemiconductor layer, in addition to the mask, by providing the barrierlayer; therefore, the semiconductor layer can be protected from water,light, or oxygen with more certainty.

An organic material is generally used to form the mask 106; therefore,the mask itself absorbs and retains water in some cases. However, thebarrier layer is provided between the mask and the semiconductor layer,and according to this, moisture of the mask is prevented frompenetrating into the semiconductor layer by the barrier layer eventhough the mask retains water. Thus, an organic TFT with higherreliability can be provided. The number of manufacturing steps is not somuch increased since the barrier layer can be etched utilizing the mask106.

In this embodiment mode, the explanation is made using a bottom gateorganic TFT shown in FIG. 1E; however, it is obvious that thisembodiment mode can be applied to a bottom gate organic TFT of FIG. 2 ora top gate organic TFT of FIG. 3D. This embodiment mode can be freelycombined with Embodiment Modes 1 to 4 within the range of enablement.

Embodiment Mode 6

In this embodiment mode, a structure for reducing deterioration of anorganic semiconductor layer caused by water, an organic gas, or the likewhich penetrates from a substrate side is explained with reference toFIGS. 9A and 9B.

In this embodiment mode, a barrier layer 901 is provided between asubstrate and an organic TFT. This barrier layer may be formed fromsilicon nitride which does not contain hydrogen formed by a radiofrequency sputtering method or a multilayer film of the silicon nitrideand a silicon oxide film. The barrier layer 901 may be formed over thewhole surface of the substrate as shown in FIG. 9A or may be selectivelyformed only over a portion in which an organic TFT is to be formed aboveas shown in FIG. 9B. After forming the barrier layer 901, the organicTFT 902 explained in Embodiment Modes 1 to 5 is formed over the barrierlayer.

This barrier layer is a barrier layer against water vapor or an organicgas which penetrate from the substrate side, which can prevent anorganic semiconductor material and the like from deterioration caused bywater vapor or an organic gas. When a structure provided with a barrierlayer between a semiconductor layer and a mask explained in EmbodimentMode 5 is applied to this embodiment mode, water vapor or an organic gascan be prevented from above and below organic semiconductor layer.

This embodiment mode can be freely combined with Embodiment Modes 1 to 5within the range of enablement.

Embodiment Mode 7

In this embodiment mode, an example in which an organic TFT of thepresent invention is formed using an organic material is described withreference to FIGS. 10A to 10C. First, a substrate 1001 having aninsulating surface is prepared as shown in FIG. 10A. The substrate 1001may have flexibility and light transmitting properties, and made of oneselected from polyethylene terephthalate (PET), polyethylene naphthalate(PEN), polyethersulfone (PEE), polycarbonate (PC), polyimide, and thelike. The practical thickness of the substrate 1001 is from 10 μm to 200μm.

A first conductive film which serves as a gate electrode 1002 of a TFTis formed over the substrate 1001 using a conductive paste. A conductivecarbon paste, a conductive silver paste, a conductive copper paste, aconductive nickel, or the like are used as the conductive paste, and theconductive paste is pattered in the predetermined shape by a screenprinting method, a roll coating method, or a droplet discharge method.After the conductive paste is formed in a predetermined pattern,leveling and drying are carried out, and then, curing is carried out ata temperature from 100° C. to 200° C.

Then, an insulating film which serves as a gate insulating film 1003 isformed over the gate electrode 1002. A first insulating film is formedfrom a material added with an acrylic resin, a polyimide resin, apolyimide resin, a phenoxy resin, a nonaromatic polyfunctionalisocyanate, a melamine resin, or the like by a roll coating method, aspray method, or the like. The gate insulating film is preferably formedso as to have a film thickness of approximately from 100 nm to 200 nm inconsideration of gate voltage.

Then, second conductive films which serves as source and drainelectrodes 1004 and 1004′ are formed over the gate insulating film 1003.As a material for the second conductive films, it is desired to usemetals having a high work function for making an ohmic contact with thesemiconductor layers, since a number of organic semiconductor materialsare P type semiconductors in which materials for transporting electriccharges transport positive holes as carriers. Concretely, the secondconductive film is formed from a conductive paste including metal suchas gold, platinum, chrome, palladium, aluminum, indium, molybdenum, ornickel, or alloys thereof by a droplet discharge method, a printingmethod, or a roll coating method.

Next, an organic semiconductor film is formed. When a high molecularweight based material is used among organic semiconductor films, adipping method, a casting method, a bar coating method, a spin coatingmethod, a spray method, a droplet discharge method, or a printing methodmay be appropriately used. An organic molecular crystal or an organichigh molecular weight compound material may be used as an organicsemiconductor material. As a specific organic molecular crystal, apolycyclic aromatic compound, a conjugated double bond-based compound,carotene, a macrocycle compound or a complex thereof, phthalocyanine, acharge transfer complex (CT complex), a TTF (tetrathiofulvalene) TCNQ(tetracyanoquinodimethane) complex, a free radical,diphenylpicrylhydrazyl, pigment, and protein can be given. On the otherhand, as a specific organic high molecular weight compound material, ahigh molecular weight material such as a π-conjugated polymer (highmolecular weight), polyvinilpyridine, an iodide complex, aphthalocyanine metal complex, or the like can be given. Especially, itis preferable to use a π-conjugated polymer (high molecular weight)having a skeleton including a conjugated double bond such aspolyacetyrene, polyaniline, polypyrrole, polythiophene derivatives,poly(3-hexylthiophene) [P3HT, that is, a high molecular weight materialthat alkyl group of polythiophene derivatives in which flexible alkylgroup is introduced to three positions of polythiophene is hexyl group],poly(3-alkylthiophene), poly(3-docosylthiophene), polyparaphenylenederivatives, or polyparaphenylene vinylene derivatives.

A vapor deposition method may be used for an organic semiconductor filmformed from a low molecular weight based material. For example, athiophene oligomer film (degree of polymerization is 6) or a pentacenefilm may be formed by a vapor deposition method.

In particular, in the case where the substrate 1001 is a largesubstrate, full of flexibility, or the like, the organic semiconductorfilm is preferably formed by the method of dropping a solution. Then, asolvent is made to vaporize by leaving naturally or baking to form asemiconductor film 1005 containing an organic material as shown in FIG.10U.

An insulating layer which is to be a mask 1006 is formed so as to be incontact with the semiconductor film 1005. The mask may be formed by adroplet discharge method or a printing method, and in addition, theshape of the mask may be exposed to light using a photomask after beingformed by a droplet discharge method. These method for forming a maskare preferable since physical damage to a semiconductor film is lessthan that of a plasma method or a sputtering method. A heat-resistanthigh molecular weight material is preferably used as the material of theinsulating layer, and a high molecular weight material which has anaromatic ring or a heterocyclic ring as a main chain and includes atleast a highly polar heteroatom group in an aliphatic portion can beused. As typical examples of such high molecular weight substances,polyvinyl alcohol (PVA), acrylic, siloxane, polyimide, and the like canbe given. When a photo mask is used as the mask 1006, a photosensitiveresin material such as an epoxy resin, a phenol resin, a novolac resin,an acrylic resin, a melamine resin, a urethane resin, or the like isused as an insulating film of a photosensitive resin. In addition,photosensitive organic materials such as benzocyclobutene, parylene,flare, and polyimide can also be used. As typical positivephotosensitive resins, a photosensitive resin having a novolac resin anda naphthoquinonediazide compound as a photosensitive agent can be given,while as typical negative photosensitive resins, a photosensitive resinhaving a base resin, diphenylsilanediol, an acid generating agent, andthe like can be given.

Then, the semiconductor film 1005 containing an organic material isetched using the mask 1006 to form a semiconductor layer 1007 containingan organic material as shown in FIG. 10C. The mask 1006 is not removedbut to remain over the semiconductor layer 1007, and thus an organic TFTis completed. After completing the organic TFT, an insulating film,passivation film, and the like are formed above the TFT to manufacture asemiconductor device.

As described above, a lightweight and flexible semiconductor device canbe obtained by an organic TFT in which all the portion thereof areformed from organic compound materials. In addition, the organic TFT canbe formed from an inexpensive organic material, and further, usabilityof the material can be heightened, and thus the cost of thesemiconductor device can be reduced. A vacuum machine is not required tobe used in a manufacturing step; therefore, a machine cost can be alsoreduced.

This embodiment mode can be freely combined with Embodiment Modes 1 to 6within the range of enablement.

Embodiment Mode 8

A method for manufacturing a display panel in a display device accordingto the present invention is explained with reference to FIGS. 11A and11B. In FIGS. 11A and 11B, as for the same reference numerals as inEmbodiment Modes 1 to 7, the material, the forming method, and the likethereof are referred to the description in Embodiment Modes 1 to 7.

Firstly, a method for manufacturing a liquid crystal display panel isexplained with reference to FIG. 11A. An organic TFT 1101 formedaccording to Embodiment Modes 1 to 4 is formed over a substrate 101, apixel electrode 1102 is formed so as to be connected to a drainelectrode 104′ included in the organic TFT 1101, and an orientation film1103 is formed over the pixel electrode 1102. A substrate 1108 providedwith a color filter 1107, an opposite electrode 1106, and an orientationfilm 1105 is prepared, and then pasted to the substrate 101 by a sealant(not shown). Then, a liquid crystal 1104 is injected to complete adisplay device provided with a display function. Polarizing plates 1100and 1109 are pasted to the substrates 101 and 1108 respectively.Further, the orientation films 1103 and 1105, and the liquid crystal1104 may be also formed by a droplet discharge method in order torealize the shortening of a manufacturing time and the reduction of amanufacturing cost.

A method for manufacturing a display panel in a display device includinga light emitting element is explained with reference to FIG. 11B. Anorganic TFT 1101 formed according to Embodiment Modes 1 to 4 is formedover a substrate 101, and an insulating layer 1110 is formed over theorganic TFT 1101. A wiring 1111 connected to a drain electrode 104′included in the organic TFT 1101 is formed, and a conductive layer 1112is formed so as to be connected to the wiring. Subsequently, aninsulating layer 1113 which is to be an embankment is formed, and anelectroluminescent layer 1114 and a conductive layer 1115 are stacked soas to be in contact with the conductive layer 1112. In the abovestructure, when the organic TFT 1101 which drives the light emittingelement is an N type organic TFT, the conductive layer 1112 correspondsto a cathode and the conductive layer 1115 corresponds to an anode.Thus, a display device which performs a so-called top emission, in whichlight from the light emitting element is emitted toward the oppositedirection of the substrate 101 side, is completed. On the other hand,when the organic TFT 1101 which drives the light emitting element is a Ptype organic TFT, the conductive layer 1112 corresponds to an anode andthe conductive layer 1115 corresponds to a cathode. Thus, a displaydevice which performs a bottom emission, in which light from the lightemitting element is emitted toward the substrate 101 side, is completed.

The display panel described in this embodiment mode is only one mode,and it is obvious that display panels having other various structurescan be manufactured. This embodiment mode can be freely combined withEmbodiment Modes 1 to 7 within the range of enablement.

Embodiment Mode 9

This embodiment mode is explained in detail with reference to FIGS. 12Aand 12B. A display device according to this embodiment mode has a pixelportion provided with an electronic ink formed from a microcapsule whichis incorporated with a contrast medium in which reflectivity changes byapplying electric field or a charged particle in which reflectivitychanges by applying electric field in each pixel, and an organic TFTcontrolling electric field which will be applied to each pixel.

FIG. 12A is a longitudinal sectional view which explains the structureof a pixel portion and FIG. 12B shows a top view. An organic TFT 1203 inwhich an organic semiconductor layer is used as explained in EmbodimentModes 1 to 7 exists between plastic substrates 1201 and 1202. Anelectron ink layer 1209 including a microcapsule 1206 incorporated witha charged particle is arranged between a pixel electrode 1204electrically connected to each organic TFT and a common electrode 1205in the opposing side of the pixel electrode. Insulating films 1210 to1212 are formed from insulating materials, and a wiring 1213electrically connects the pixel electrode 1204 and the organic TFT 1203.The longitudinal sectional view shown in FIG. 12A corresponds to lineA-A′ shown in FIG. 12B.

At least one of the plastic substrates 1201 and 1202 has lighttransmitting property, and the material thereof is selected frompolyethylene terephthalate (PET), polyethylenenaphthalate (PEN),polyethersulfone (PES), polycarbonate (PC), polyimide, and the like. Theplastic substrates preferably have flexibility, and the practicalthickness thereof is from 10 μm to 200 μm. The embodiment of theinvention is not essentially affected even if the thickness of theplastic substrate increases to be greater than the above describedrange, as a matter of course.

Barrier layers 1207 and 1208 are formed from an inorganic insulatingmaterial over the surface of the plastic substrates 1201 and 1202 so asto have a film thickness of from 10 μnm to 200 nm. This is anAlO_(x)N_(1-x) (x=from 0.01 atomic % to 20 atomic %) film, a layerformed from silicon nitride which does not contain hydrogen formed by aradio frequency sputtering method using silicon as a target and usingnitrogen as a sputtering gas, or a stacked layer structure includingeither of the two. This inorganic insulating material is preciselyformed to be used as a barrier layer against water vapor and an organicgas which penetrate from external environment. The barrier layers areformed to prevent an organic semiconductor material and themicrocapsule, which is incorporated with a contrast medium in whichreflectivity changes by applying electric field or the charged particlein which reflectivity changes by applying electric field, fromdeteriorating by water vapor or an organic gas.

This embodiment mode can be freely combined with Embodiment Modes 1 to 8within the range of enablement.

Embodiment Mode 10

As an example of an electronic device manufactured by applying thepresent invention, the following devices can be given: a digital camera;a sound reproducing device such as a car audio; a personal computer; agame machine; a personal digital assistant (cellular phone, portablegaming machine, or the like); an image reproducing device provided witha recording medium such as a home video game machine; and the like. Aspecific example of these electronic devices is shown in FIGS. 13A to14C.

FIG. 13A shows a TV set, which includes a chassis 9501, a displayportion 9502, and the like. FIG. 13B shows a monitor for a personalcomputer, which includes a chassis 9601, a display portion 9602, and thelike. FIG. 13C shows a personal computer, which includes a chassis 9801,a display portion 9802, and the like. The invention is applied to themanufacturing of a display portion of the above electronic device. Anorganic TFT according to the invention is hardly deteriorated and ishigh reliable; therefore, a display device in which a display is hardlydeteriorated can be provided. In addition, the organic TFT according tothe invention can be formed from an inexpensive organic material, and anexpensive vacuum machine is not required to be used in a manufacturingstep by utilizing a printing method or a droplet discharge method;therefore, these electronic devices can be inexpensively manufactured.

FIG. 14A shows a cellular phone among portable terminals, which includesa chassis 9101, a display portion 9102, and the like. FIG. 14B is a PDAamong portable terminals, which includes a chassis 9201, a displayportion 9202, and the like. FIG. 14C shows a video camera, whichincludes display portions 9701 and 9702, and the like. The invention isapplied to the manufacturing of a display portion of the aboveelectronic device. An organic TFT according to the invention is hardlydeteriorated and is high reliable; therefore, a display device in whicha display is hardly deteriorated can be provided. The above electronicdevices are portable terminals; therefore, the screen thereof iscomparatively miniaturized. Hence, it is preferable to attainminiaturization by mounting a driver circuit and a functional circuitsuch as a CPU using a thin film transistor in which a polycrystallinesemiconductor is used as a channel, and a multilayer wiring over thesame substrate as the display portion. The organic TFT according to theinvention can be formed from an inexpensive organic material, and anexpensive vacuum machine is not required to be used in a manufacturingstep by utilizing a printing method or a droplet discharge method;therefore, these electronic devices can be inexpensively manufactured.Further, the above electronic devices are portable terminals; therefore,a display portion using a light emitting element may be used in order toadd value in respect of thinning, lightweight, and miniaturization. Thisembodiment mode can be freely combined with the above embodiment modeswithin the range of enablement.

This application is based on Japanese Patent Application serial No.2004-251926 field in Japan Patent Office on Aug. 31, 2004, the contentsof which are hereby incorporated by reference.

1. A method for manufacturing a semiconductor device comprising the steps of: forming source and drain electrodes over a substrate having an insulating surface; forming a semiconductor film containing an organic material over the source and drain electrodes; forming a mask over the semiconductor film; etching the semiconductor film by using the mask to form a semiconductor layer; and forming a gate electrode over the mask.
 2. The method for manufacturing the semiconductor device according to claim 1, wherein the mask comprises an organic material.
 3. The method for manufacturing the semiconductor device according to claim 1, further comprising a step of forming a barrier layer over the substrate before forming the source and drain electrodes.
 4. The method for manufacturing the semiconductor device according to claim 1, wherein the etching step is performed by O₂ ashing or O₃ ashing.
 5. A method for manufacturing a semiconductor device comprising the steps of: forming source and drain electrodes over a substrate having an insulating surface; forming a semiconductor film containing an organic material over the source and drain electrodes; forming an inorganic film over the semiconductor film; forming a mask over the inorganic film; etching the inorganic film by using the mask to form a barrier layer, after forming the barrier layer, etching the semiconductor film by using the mask to form a semiconductor layer; and forming a gate electrode over the mask.
 6. The method for manufacturing the semiconductor device according to claim 5, wherein the mask comprises an organic material.
 7. The method for manufacturing the semiconductor device according to claim 5, further comprising a step of forming a second barrier layer over the substrate before forming the source and drain electrodes.
 8. The method for manufacturing the semiconductor device according to claim 5, wherein the etching steps are performed by O₂ ashing or O₃ ashing.
 9. A method for manufacturing a semiconductor device comprising the steps of: forming source and drain electrodes over a substrate having an insulating surface; forming a semiconductor film containing an organic material over the source and drain electrodes; forming a mask over the semiconductor film by a droplet discharge method; etching the semiconductor film by using the mask to form a semiconductor layer; and forming a gate electrode over the mask.
 10. The method for manufacturing the semiconductor device according to claim 9, wherein the mask comprises an organic material.
 11. The method for manufacturing the semiconductor device according to claim 9, further comprising a step of forming a barrier layer over the substrate before forming the source and drain electrodes.
 12. The method for manufacturing the semiconductor device according to claim 9, wherein the etching step is performed by O₂ ashing or O₃ ashing.
 13. A method for manufacturing a semiconductor device comprising the steps of: forming source and drain electrodes over a substrate having an insulating surface; forming a semiconductor film containing an organic material over the source and drain electrodes; forming an inorganic film over the semiconductor film; forming a mask over the inorganic film by a droplet discharge method; etching the inorganic film by using the mask to form a barrier layer, after forming the barrier layer, etching the semiconductor film by using the mask to form a semiconductor layer; and forming a gate electrode over the mask.
 14. The method for manufacturing the semiconductor device according to claim 13, wherein the mask comprises an organic material.
 15. The method for manufacturing the semiconductor device according to claim 13, further comprising a step of forming a second barrier layer over the substrate before forming the source and drain electrodes.
 16. The method for manufacturing the semiconductor device according to claim 13, wherein the etching steps are performed by O₂ ashing or O₃ ashing. 